//将独立的不依赖于index的文件抽取出来

//返回按钮的颜色转换
var back = $$(".png0");
for (var i = 0, len = back.length; i < len; i++) {
	back[i].onmouseover = function  () {
		this.setAttribute("src", "img/return.png");
	}
	back[i].onmouseout = function () {
		this.setAttribute("src", "img/back.png");
	}
}